Acoustical coupler



26, 1967 J. H. VOGELMAN ACOUSTICAL COUPLER Filed Aug. 2, 1965 FIG.

INVENTOR JUSEP/l Mme/w wmmv BY m,

ATTORNEY United States Patent 3,360,071 ACOUSTICAL COUPLER JosephHerbert Vogelman, Roslyn, N.Y., assignor t0 Chromalloy Corporation, WestNyack, N.Y. Filed Aug. 2, 1965, Ser. No. 476,372 4 Claims. (Cl. 181-.5)

ABSTRACT OF THE DISCLOSURE transducers.

The present invention relates to a device for coupling the output of anelectrical-to-acoustical transducer, such as a loudspeaker, to the inputof an acoustical-to-electrical transducer, such as a microphone.

Often in communications systems information must be transferred withoutan actual physical connection to the existing electrical circuitry. Forexample, it may be desired to transmit the voice of an incoming call toa telephone to some remote location via a wireless radio frequencysystem or, alternatively, to transmit the voice of an incoming signal toa radio frequency receiver to some remote location via a telephonesystem. In many areas, the telephone companies prohibit actual physicalconnections to be made to the existing telephone circuitry.

In the past, in such situations electromagnetic and electrostatic pickupdevices have been used since such devices do not require an actualconnection to the circuitry. There are, however, many instances wheresuch devices may not be used or are undesirable for one reason oranother. Where, for example, a carbon or crystal microphone is beingused in the system to which the information is to be transferred,neither an electrostatic nor an electromagnetic pickup device may beemployed since both the carbon and crystal microphones are purelypressure sensitive devices. In addition, where the electric and magneticfields to which the electrostatic and electromagnetic devices respondare inaccessible or these fields are too weak to be sensed by thesedevices, electrostatic and electromagnetic pickup devices may not beused.

In the past some attempts have been made to acoustically couple theoutput of a loudspeaker to the input of a microphone. Generally, thedevices employed were air tubes arranged to couple as much of the soundas possible and limit the energy loss to a minimum. No adequateconsideration was given to the development of a proper acousticalimpedance transformation between the two transducers. Without the properimpedance transformation the sound being coupled is apt to be distorted,thereby subjecting a listener to discomfort or if the distortion isgreat there is a loss in intelligibility.

It is an object of the present invention to provide a new and improvedacoustical coupler.

A feature of an acoustical coupler constructed in accordance with thepresent invention is that a wide range of desired acoustical impedancetransformations may be developed between the two transducers beingcoupled together. Where an accurate reproduction of the sound 3,360,071Patented Dec. 26, 1967 emanating from a loudspeaker is desired, thecoupler is arranged to provide an optimized acoustical impedancetransformation. If, on the other hand, accentuation of certain portionsof the audio frequency range is desired, the accoustical cou ler may bearranged to have a shaped frequency response.

Another feature of an acoustical coupler constructed in accordance withthe present invention is that the sound is coupled with little or noenergy loss. Thus, low-level sounds are not lost in the coupling.

It is a further object of the present invention to provide a new andimproved acoustical coupler which is simple in construction andinexpensive to fabricate.

One acoustical coupler constructed in accordance with the presentinvention, to be described hereinbelow, in cludes a first surface ofselected material for forming a first cavity with the acoustical chamberof an electricalto-acoustical transducer and a second surface ofselected material for forming a second cavity with the acousticalchamber of an acoustical-to-electrical transducer. This coupler alsoincludes a passageway running from the first surface to the secondsurface for interconnecting the first and second cavities. The hardnessof the first and second surfaces and the shapes and dimensions of thefirst and second surfaces and the passageway are so selected that adesired acoustical impedance transformation is developed between the twotransducers.

For a better understanding of the present invention, together with otherand further objects thereof, reference is made to the followingdescription, taken in connection with accompanying drawing, and itsscope will be pointed out in the appended claims.

Referring to the drawing:

FIGURE 1 is a perspective view of one embodiment of an acousticalcoupler constructed in accordance with the present invention;

FIGURE 2 is a cross-section view taken along line 2-2 of FIGURE 1; and

FIGURE 3, partially in section, shows the acoustical coupler of FIGURES1 and 2 interposed between a loudspeaker and the mouthpiece of atelephone.

Referring to the drawing, an acoustical coupler constructed inaccordance with the present invention and designated generally byreference numeral 9' includes first and second surfaces 10 and 20,respectively, each of particularly selected materials. Surface 10 is thebottom surface, as viewed in FIGURES 1 and 2, of a member 13 which, forthe embodiment illustrated, is substantially fiat. Surface 20 is theinside surface of a member 23 which, for the embodiment illustrated, issubstantially cup-shaped. Member 23 is provided with a flanged rimportion 24 along its open end. Members 13 and 23 are made of a softmaterial such as 30 Durometer neoprene. As will become apparent from thedescription that follows, members 13 and 23 may be both of the samematerial or of different materials.

Members 13 and 23 are joined together along a line designated byreference numeral 30. For the construction illustrated the two membersare preferably formed as a single unit. Passing through members 13 and23 and running from surface 10' to surface 20 is a passageway 31 ofcircular cross-section for the embodiment illus trated.

FIGURE 3 shows how the acoustical coupler 9 may be interposed between aloudspeaker 12 and the microphone 22 in the mouthpiece 25 of a telephonehandset 26. Surface 10 of member 13 serves to form a first cavity withthe acoustical chamber of the loudspeaker 12 as surface 10 is positionedagainst the rim 12a of the loudspeaker. The cavity formed by theacoustical chamber of the loudspeaker 12 and the surface 10 correspondsto the space 11 within the acoustical chamber of the loudspeaker.

Surface 20 serves to form a second cavity with the acoustical chamber ofthe microphone 22 as the flanged rim portion 24 of member 23 ispositioned against the rim of the mouthpiece 25. The cavity formed bythe acoustical chamber of the microphone 22 and the surface 20corresponds to the space 21 bounded by surface 20 and the relativelyshallow space within the acoustical chamber of the microphone. Althoughthe mouthpiece structure and the narrow passages 27 in the mouthpieceserve merely to support the microphone and permit the passage of soundto the microphone, the passages 27 are also part of the cavity formed bythe acoustical chamber of the microphone and the surface 20. In thisconnection, there is apt to be an addition to the cavity 11 if theloudspeaker 12 were mounted for support in some suitable structure. Insuch a case, the member 13 could not be positioned flush against the rim12a.

The acoustical coupler 9 operates by converting a volume source, inparticular, cavity 11 within the loudspeaker 12, into a point orcylindrical source, in particular, the passageway 31. The sound wavespass through the passageway 31 and enter cavity 21 by acousticdiffraction. By providing air-tight fits at the points at which thesurface bears against the rim 12a and the flanged rim 24 bears againstthe mouthpiece 25, leakage into or out of the chamber is preventedthereby reducing the introduction of distortion and the possibility ofany energy loss in the coupling.

The particular acoustical impedance transformation effected between anytwo transducers by an acoustical coupler constructed in accordance withthe present invention is dependent upon the materials used for surfaces10 and 20 and members 13 and 23, the shapes and dimensions of thesurfaces 10 and 20 and members 13 and 23, the shape and dimensions ofthe passageway 31, and the shapes, dimensions and materials employed inthe acoustical chambers of the two transducers. It is within the scopeof the present invention to select whatever appropriate materials,shapes and dimensions are needed for the variables just enumerated toarrive at the desired combination which will provide the desiredacoustical impedance transformation between two selected transducers.The various parameters are interdependent so that the same impedancetransformation is possible with a number of different combinations. Theselection of materials, shapes and dimensions is dependent upon thecombined effect of the values selected and the desired acousticalimpedance transformation. In one application, it may be desired tosupply to the microphone 22 an accurate reproduction of the soundemanating from the loudspeaker 12 in which case the acoustical coupler 9is designed to have an optimized acoustical impedance transformation. Onthe other hand, where it is desired to accentuate certain portions ofthe audio frequency range and to attenuate other portions, theacoustical coupler may be designed to have a shaped frequency response.Generally, the cross-sectional areas of the members 13 and 23 will besubstantially greater than the crosssectional area of the passageway 31.The cross-sectional area of the passageway 31 is proportional to thelowest wavelength which is to be passed by the coupler. Thus, for lowerwavelengths, the passageway 31 is made larger.

The following values have been found especially advantageous for theparticular application described herein, resulting in a passbandextending from 300 c.p.s. to 3000 c.p.s.:

Material of members 13 and 23, 3O Durometer neoprene.

O.D. member 13, 2%

Thickness of member 13,

Center of curvature of member 23, 1.45" from surface 16 along axis ofpassageway 31.

Inside radius of member 23, 1.264".

Thickness of member 23, di

4 O.D. flanged rim portion 24, 3 LD. flanged rim portion 24, 2%Thickness of flanged rim portion 24, 0.62. Diameter of passageway 31,Angle between plane of flanged rim portion 24 and plane of member 13,15.

While there has been described what is at present considered to be thepreferred embodiment of this invention it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the invention and it is, therefore, aimedto cover all such changes and modifications as fall within the truespirit and scope of the invention.

What is claimed is:

1. Sound coupling apparatus comprising: first and second transducerunits, one of said units including sound translating means of the typeoperable by electrical input signals to produce corresponding soundsignals, the other of said units including sound translating means ofthe type operable by sound signals to produce corresponding electricaloutput signals; an acoustical coupler between said transducer units totransfer sound energy between the respective sound translating meansthereof, said coupler including a first part of generally cup-shapedconfiguration and provided with a first engagement surface around themouth of the cup, said engagement surface being engaged with acorresponding surface of said first transducer unit, the soundtranslating means of said first transducer unit being positionedadjacent the mouth of said cup-shaped part to serve as one wall of afirst cavity within the interior spaces of said cup-shaped part; saidcup-shaped part being provided with a passageway one end of whichcommunicates with said first cavity near the bottom of the cup at leastapproximately opposite the sound translating means of said firsttransducer unit, said passageway having a small cross-sectional areaadapted to conduct sound energy; said coupler further including a secondpart integral with said cup-shaped part and presenting a secondengagement surface surrounding the other end of said small passageway,said second engagement surface being engaged with a correspondingsurface of said second transducer unit, said second transducer unitbeing formed to define a second cavity with the sound translating meansof said second transducer unit serving as one wall of said second cavityopposite said other end of said small passageway, said first and secondcavities having cross-sectional areas substantially greater than that ofsaid passageway and providing acoustic communication between both soundtranslating means through said passageway.

2. Apparatus as in claim 1, wherein said first engagement surfacecomprises a substantially planar flange portion extending around themouth of said cup-shaped part.

3. Apparatus as in claim 2, wherein said second engagement surface issubstantially planar.

4. Sound translating apparatus comprising: an electrical-to-acousticaltransducer with sound producing means operable by electrical inputsignals; an acousticalto-electrical transducer with sound-responsivemeans for producing electrical output signals corresponding to receivedsound signals; acoustical coupling means disposed between saidtransducers to transfer sound energy from one to the other with highefiiciency and desired frequency-response characteristics, said couplingmeans including first wall means contiguous with saidelectricaltoacoustical transducer to form a first cavity having at oneend the sound-producing means of said transducer and provided at anopposite end with an opening defining a passageway for conducting soundwaves out from said first cavity, the interior surfaces of said firstwall means presenting an imperforate sealed enclosure for said firstcavity extending continuously from the periphery of said sound-producingmeans to the edges of said passageway opening so as to prevent thetransmission of sound energy out from said first cavity other thanthrough said 5 passageway; said coupling means further including secondwall means contiguous with said acoustical-to-electrical transducer toform a second cavity having at one end an opening to said passageway andhaving at an opposite end the sound-responsive means of saidacoustical-to-electrical transducer, the interior surfaces of saidsecond wall means presenting an imperforate sealed enclosure for saidsecond cavity extending continuously from the edges of said passagewayopening to the periphery of said sound-responsive means so as to preventloss of sound energy from said second cavity, said passageway providingan enclosed communication channel between said cavities having across-sectional area substantially smaller than the cross-sectionalareas of either of said cavities to serve as an efiectively point sourceof sound energy for transmitting sound waves by acoustic diffractionfrom the sealed volume of said first cavity to the sealed volume of saidsecond cavity.

References Cited UNITED STATES PATENTS 19,694 3/1858 Gies 4166 1,204,13611/1916 Creveling 179-182 2,552,970 5/1951 Horsley et al. 181.5 X3,058,539 10/1962 Adler 181-.5 1,145,751 7/1915 Creveling 179-182FOREIGN PATENTS 620,695 3/ 1949 Great Britain.

BENJAMIN A. BORCHELT, Primary Examiner. M. F. HUBLER, AssistantExaminer.

1. SOUND COUPLING APPARATUS COMPRISING: FIRST AND SECOND TRANSDUCERUNITS, ONE OF SAID UNITS INCLUDING SOUND TRANSLATING MEANS OF THE TYPEOPERABLE BY ELECTRICAL INPUT SIGNALS TO PRODUCE CORRESPONDING SOUNDSIGNALS, THE OTHER OF SAID UNITS INCLUDING SOUND TRANSLATING MEANS OFTHE TYPE OPERABLE BY SOUND SIGNALS TO PRODUCE CORRESPONDING ELECTRICALOUTPUT SIGNALS; AN ACOUSTICAL COUPLER BETWEEN SAID TRANSDUCER UNITS TOTRANSFER SOUND ENERGY BETWEEN THE RESPECTIVE SOUND TRANSLATING MEANSTHEREOF, SAID COUPLER INCLUDING A FIRST PART OF GENERALLY CUP-SHAPEDCONFIGURATION AND PROVIDED WITH A FIRST ENGAGEMENT SURFACE AROUND THEMOUTH OF THE CUP, SAID ENGAGEMENT SURFACE BEING ENGAGED WITH ACORRESPONDING SURFACE OF SAID FIRST TRANSDUCER UNIT, THE SOUNDTRANSLATING MEANS OF SAID FIRST TRANSDUCER UNIT BEING POSITIONEDADJACENT THE MOUTH OF SAID CUP-SHAPED PART TO SERVE AS ONE WALL OF AFIRST CAVITY WITHIN THE INTERIOR SPACES OF SAID CUP-SHAPED PART; SAIDCUP-SHAPED PART BEING PROVIDED WITH A PASSAGEWAY ONE END OF WHICHCOMMUNICATES WITH SAID FIRST CAVITY NEAR THE BOTTOM OF THE CUP AT LEASTAPPROXIMATELY OPPOSITE THE SOUND TRANSLATING MEANS OF SAID FIRSTTRANSDUCER UNIT, SAID PASSAGEWAY HAVING A SMALL CROSS-SECTIONAL AREAADAPTED TO CONDUCT SOUND ENERGY; SAID COUPLER FURTHER INCLUDING A SECONDPART INTEGRAL WITH SAID CUP-SHAPED PART AND PRESENTING A SECONDENGAGEMENT SURFACE SURROUNDING THE OTHER END OF SAID SMALL PASSAGEWAY,SAID SECOND ENGAGEMENT SURFACE BEING ENGAGED WITH A CORRESPONSINGSURFACE OF SAID SECOND TRANSDUCER UNIT, SAID SECOND TRANSDUCER UNITBEING FORMED TO DEFINE A SECOND CAVITY WITH THE SOUND TRANSLATING MEANSOF SAID SECOND TRANSDUCER UNIT SERVING AS ONE WALL OF SAID SECOND CAVITYOPPOSITE SAID OTHER END OF SAID SMALL PASSAGEWAY, SAID FIRST AND SECONDCAVITIES HAVING CROSS-SECTIONAL AREAS SUBSTANTIALLY GREATER THAN THAT OFSAID PASSAGEWAY AND PROVIDING ACOUSTIC COMMUNICATION BETWEEN BOTH SOUNDTRANSLATING MEANS THROUGH SAID PASSAGEWAY.